The overall goal of this proposal is to study the mechanisms underlying the immunologic immaturity of the murine neonate. A variety of physical and serological techniques will be employed to isolate neonate cell pupulations. From this panel of cells, we will then attempt to characterize the cells responsible for accessory and natural killer (NK) activities, as well as other cell types that inhibit these activities. These methods to be employed include adherence, density gradient centrifugation cell sorting and in vitro culture with various growth factors (IL-2, IL-3, M0 growth factor) including a stimulatory factor(s) from mouse amniotic fluid (MAF). We propose to study whether suppressor cells which have already been identified in the eneonate, inhibit via a prostaglandin (PGE) mediated effect on Ia expression and/or via other soluble factors. The relationship, if any between M0 suppressors, T suppressors (Ts) and the accessory cell deficiency will be explored. Whether M0, dendritic cells, and/or epithelial cells are the predominant accessory cells found in the neonate thymus will be examined. These latter experiments bear on the role of the thymus in selecting the T-cell repertoire. Neonatal suppression has also been attributed to circulating soluble factors such as alphafetoprotein (AFP). We propose to isolate the suppressive components from MAF and determine whether their activity is mediated via M0 and/or Ts. The phenotypic characteristics of the cells induced by MAF will be compared (using MAb's and flow cytometry) with those isolated from the neonate. The role of PCE as well as non PGE suppressors will also be explored in this system. Recently, we observed that Cu++ modulates suppression by AFP and a series of experiments are outlined on the role of Cu++ in neonate immunosuppression. In addition, factors which stimulate the growth of neonate and a small subpopulation of adult spleen cells have been identified in MAF. Experiments are planned to isolate the stimulatory factor(s) by HPLC and to determine the spectrum of cells affected (particularly whether suppressor M0 and/or Ts are stimulated). The work outlined is pertinent to the hypothesis that the decline of circulating inhibitory factors in the postnatal period is responsible for the acquisition of positive immunity in the young adults. These studies are also relevant to immunosuppression in pregnancy and disease states where high circulating levels of AFP are found.